Mercury switch



July 28, 1942.

N. H. FREEMAN MERCURY SWITCH Filed Aug. 5, 1940 INVENTOR NAT HARRIS FREFMAN BY 91m w aazzm ATTORNEYS Patented Jul 'zs, 1942 Application August 5, 1940, Serial No. 351,537

7 In Great Britain August 1, 1939 3 Claims (01300-141) This invention relates to temperature control v devices of the kind wherein variations in temperature within a furnace or the like are communicated through an expansible fluid to a mer= .cury operated switch adapted to open or close an electrical circuit arranged toactuate means for increasing or diminishing the furnace temperature and thereby restore such temperature to a'predetermined level.

The object of the present invention is to provide improvements relating to the mercury switch in apparatus of the kind above indicated where- 'by "certain disadvantages experienced in theworking of such apparatus are avoided.

According to the present invention temperature control apparatus of the kind above described is provided wherein the operative parts of the mercury switch are at all times immersed in a liquid such as a hydrocarbon which will prevent xidisation at the point of electrical on tact.

Reference will now be made to the accompanying drawing which illustrates diagrammatically and by way of example a temperature control device constructed according to the invention.

In the device illustrated variations of temperature within a furnace chamber or the like are transmitted by means of a phial 0 containing an expansiblefluid disposed within said chamber and communicating by --means of a conduit 1) and passage c with one end of a tube d containing a body ofmercury constituting one terminal of the electrical control circuit. a Thepassage c is formed through a plate fixed toa supporting panel I and the tube at is fixed into a rotatable spigot g mounted in the plate e, the said spigot being hollow and having a port which maintains constant communi-r cation with the passage 0 in all positions of angular adjustment ofthe tube d, which adjustment is obtained by rotating a knob'or hand wheel h.

Rotatable with, the spigot g is a bracket 1 electrically insulated from the saidspigot and plate a, the said bracket carrying the second terminal of the control circuit which consists of a rod or wire 7' which enters the end of the .tube d remote from its mounting in the spigot g. The said rod or wire :i is bent as shown to form a parallel portion"): which is fixed in a carrier 1 movable along a guide rod mcarried in a flanged portion nof the bracket 1. Extending through the flange n-and also engaging the carrier 1 is a screw threaded adjusting rod oiwhich is held against which the mercury rises sumciently within its tube and makes contact with the end of the rod or wire 1' and complete the electrical controlling circuit. This circuit includes wires p and q connected respectively to the plate e and to the flange n and which lead to a relay or other device by which the temperature control is etlected.

For-the purpose'of preventing dust or other foreign matter from interfering with the operation of the device above described and to prevent arcing and corresponding oxidisation of the metal wire or rod Lthe tube d is provided with a branch 1' for the attachment thereto of a flexible connection a leading to a reservoir t from which that portion of the tube d which is not occupied by the mercury is kept filled with a liquid hydrocarbon so that both contacts, mercury'and the adjustable wire 7 are always immers'ed in such hydrocarbon. The outer end of the tube (1 has a closure element u which may conveniently be of a synthetic rubber material capable of making a fluid tight joint'whilst permitting adjusting movement of the wire or rod 7'.- As it has been found in practice that oxidisation can interfere to a serious extent with the correct functioning of the apparatus, the invention provides a simple and effective means of ensuring greater accuracy and a more strict control than has been possible hitherto, of the temperature within a furnace chamber or the like.

The conduit b communicates with a three-way connection 22 mounted on the plate e, and connected through a conduit w with a liquid seal a:

which constitutes a safety valve to allow gas or air under pressure to escape from the conduit b and plurality of differently inclined positions, a conduit connected to said'tube and containing a fluid expansible in response to variations in temperature, a body of mercury in said tube movable axialmovement so that as it is rotated the car 5 under the influence of said fluid, an electrical a contact element projecting 'intoone end of said tube and engageable by the mercury, means for supporting'saidcontacteiementexteriorlyoithe tube, for adjustment therewith, a sideportinsaidtubeai'iaiblepipeconnectedto saidportandextendingupwardly,andanonconductive liquid hydrocarbon'contnined in said tube over said mercury, said being hydrocarbon capable of preventing oxidation oi said contact,

and said pipe containingga body 0! said hydrocarbonand beingoperabletomaintainahydr'ostatichead onsaid hydrocarboninsaidtubc'inall adjusted positions at the latter. andwithout interi'ering with tilting movement orsaid tube,

2. The temperature control device defined in claim 1, wherein said contact element is spaced from the walls of said tube and sealing means are provided between the latter andsaid contact .element for preventing leakage 01 said hydrocarbon from said tube;

3. Inamerwryswitchdcvice-ahibemmmted ataninclinstiontcthehorinontalandcontaming mercuryadaptedtoberaisedandloweredbyiiuid pressure introduced adjacent the bottom at the tube,theiatterhavingmmpenupper-end,acoutact element projecting into the open mouth of rsaidtubeanddisposedmbctantiallypa'rallelto themsthereorandadaptedtobecontactcd-by themercuryandcloseanelectrical circuits. liquid hydrocarbondisposedinsaidtubeoverthe body oi mercury. means supporting said contact element for longitudinal movement. for predeterminingtheheightoi'mercuryatwhichthecircuit will becloced, anda closure member dlsposedinthemouthoisaidtubeandsealinglyassociated with said contact element, and being operable to prevent egress of said hydrocarbon while permitting free adjustment or said contact clement lengthwise oisaid tube.

NAT HARRIS FREEMAN.- 

